Physico-chemical properties and photo-reactivity relationship for para-substituted phenols in photo-assisted Fenton system

The reactivity of phenolic compounds can be drastically affected by the electronic nature of the substituting groups. In this work, the effect of physico-chemical properties on the reactivity via photo-assisted Fenton catalysis is reported for several para-substituted phenols (p-nitrophenol (p-NO2), p-chlorophenol (p-Cl), p-hydroxybenzaldehyde (p-CHO), phenol (p-H), p-methoxyphenol (p-OCH3), p-hydroxyphenol (p-OH)) in order to cover a wide range of electronics effects. Electronic descriptors (Hammett constants (sigma). frontier molecular orbital energies (E-HOMO), electronic and zero point energies (E, E-ZERO)). electrochemical descriptor (half wave potential for the oxidation of phenols to phenoxyl radical (E-1/2)), and other descriptors (acidity constants (pK(a)), maximum absorption wavelength (lambda(max)), 1-octanol/water partition coefficient (K-ow)) were correlated with the initial Fenton and photo-Fenton degradation rates (r(0)). Linear relationships were obtained between the initial Fenton and photo-Fenton degradation rates and electronic descriptors. However p-Cl and p-CHO showed higher photo-Fenton degradation rates than ones predicted by the model implying the presence of weaker bonds in these molecules. The biodegradability increase due to the photo-Fenton process was strong but poorly selective suggesting that the produced intermediates present a similar biodegradability. (C) 2009 Elsevier B.V. All rights reserved

Improvement of high temperature corrosion resistance of tool steels by nanostructured PVD coatings

International audienceDeposits elaborated by PVD processes are of great importance in mechanical industry, which requires high performance tools with always increasing lifetime. Outstanding physical and chemical properties have been recently obtained with a new generation of coatings, characterized by the coexistence of two nanometric phases. Such phase distribution is achieved either by successive deposition of nanolayers of different nature (named multilayer or 2D material) or by dispersing crystalline nanodomains into an amorphous matrix (named nanocomposite or 3D material). Deposited onto tool steels, these coatings can be a solution to sustain high stresses encountered in severe machining because, in such conditions, coated parts have not only to fulfil high tribologic properties, but also to be thermally resistant. This paper presents some data concerning the oxidation behaviour of coated pieces in relation to the coating nanostructure. Nanocomposite magnetron sputtered TiBN, as well as arc evaporated multilayered TiN/CrN deposits are investigated in comparison with microstructured TiAlN, TiN or CrN layers. Nature of oxides developed during 24 hours at 700°C in air is determined by XRD and observed by SEM, while protective potentialities (oxidation critical temperature and kinetic parameters) are deduced from thermogravimetric analysis. Whatever the configuration, 2D or 3D, a beneficial influence of the nanostructure is observed on the corrosion resistance at high temperature. Corrosion rates are particularly decreased for CrN base coatings, whereas TiN coating leads to a thick cracked rutile layer, damaging from an oxidation point of view. Oxidation protection due to multilayered CrN/TiN deposit is significant, which is explained by the fact that, the formed Cr2O3 layer is a barrier against the progression of the oxide layer

Improvement of the corrosion resistance of low oxynitrided steel by a polymer impregnation post treatment

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Comparative evaluation of polymer surface functionalization techniques before iron oxide deposition. Activity of the iron oxide-coated polymer films in the photo-assisted degradation of organic pollutants and inactivation of bacteria

The preparation of iron oxide-coated polymer films and their photocatalytic activity in organic pollutants degradation and bacterial inactivation is described. Polyvinyl fluoride (PVF), polyethylene (PE) and polyethylene terephtalate (PET) films were used as catalyst supports. Polymer surfaces were functionalized by vacuum-UV radiation (V-UV) and radio-frequency plasma (RF-P); and also by photo-Fenton oxidation (P-FO) and TiO2 photocatalysis (Ti-PC) in solution. These pre-treatments were performed to improve iron oxide adhesion on the commercial polymer surface. The functionalized polymers films (P-f) were afterward immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl3. The photocatalytic activities of iron oxide-coated functionalized polymers films (P-f-Fe oxide) prepared by different methods were compared during hydroquinone degradation in presence of H2O2. RF-P and Ti-PC pre-treated polymers showed significantly higher photocatalytic activity and long-term stability during processes leading to pollutant abatement, if compared with not treated ones (NT), although similar leaching of iron was observed for all the materials. PET bottles (PETb) were used as reactor and catalyst supports. The produced PETbf-Fe oxide surfaces were efficient in photo-assisted bacterial inactivation in the presence of H2O2, and no dissolved iron species were detected in solution. (C) 2010 Elsevier B.V. All rights reserved

On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic stainless steel in acid and neutral solutions

International audienceUniform corrosion of steels is responsible for the early damaging of many industrial parts and its control and monitoring prevent against significant economic and environmental failures. Yet, classical estimation of corrosion damage gives only the result of the average corrosion rate but not the 'instantaneous' value. In that context, acou stic emission (AE) technique, based on the rapid release of energy within a material generating a transient elastic wave propagation, was carried out to get quantitative information on corrosion evolution. Uniform corrosion conditions close to industrial ones were simulated with the use of a pilot device, allowing the simultaneous control and measurement of the temperature and pH of the saline and/or acidic solutions, as well as the amount of dissolved oxygen and the fluid velocity, together with AE recordings. Emission so urces during uniform corrosion of carbon steel and austenitic stainless steel were then identified as hydrogen release, friction of hydrogen bubbles and evolution of corrosion deposits, each of these mechanisms inducing the emission of AE signals with specific parameters. Moreover, it appears clearly that acoustic emission measurements are in good correlation with aggressiveness of the corrosive media, and a semi-quantitative correlation is obtained between AE activity and corrosion rate for austenitic stainless steel. Whereas initial surface conditions greatly influence the acoustic activity, AE monitoring appears to be a rewarding technique for detecting corrosion rate evolutions during process modifications